Dpcch and hs-dpcch control at low grants for e-dch

ABSTRACT

Disclosed is a method and an enhanced uplink (UL) telecommunication system for power control. The system comprises at least one first radio network controller (RNC) and at least one first base station, which enables wireless communication with at least one first user terminal. The power for an uplink Dedicated Physical Control Channel (DPCCH) in a first enhanced UL transport channel (E-DCH) is controlled. The control is made by the first base station on the basis of a signal to interference ratio (SIR) target value sent by the first RNC. Thereby, the SIR real time value for the UL DPCCH is controlled towards the target value. The first user terminal and the first base station further calculate a power for at least an Enhanced Dedicated Physical Data Channel (E-DPDCH) in the first E-DCH, which power is defined as the sum of the DPCCH power and a power offset. The calculation is at least based on a power offset configuration and an absolute grant provided by the first base station, which grant at least set the maximum E-DPDCH power. The first user terminal further transmits the uplink data traffic on the first E-DCH with the controlled DPCCH power and the calculated E-DPDCH power. When the first base station and the first user terminal detects that the E-DPDCH absolute grant is reduced below or increased above a grant threshold, the base station changes the SIR target value. Further, the first base station and the first user terminal compensates the change of the target value by recalculating at least the E-DPDCH power so that the power reflects both the changed DPCCH power resulting from the changed SIR target value and the improvement due to optimized channel estimation in case of changed SIR real time value.

TECHNICAL FIELD

The present invention relates to a method and a telecommunication systemfor power control, and a base station and a user terminal in the systemenabling said method.

BACKGROUND

There is an increasing need of delivering wireless technology withbroadband capacity for cellular networks. A good broadband system mustfulfil certain criteria, such as high data rate and capacity, low costper bit, good Quality of Service and greater coverage. High Speed PacketAccess (HSPA) is an example of a network access technology that enablesthis.

HSPA is a collection of protocols which improves the performance ofexisting Universal Mobile Telecommunication Systems (UMTS), which is athird generation (3G) cell phone technology. UMTS uses Wideband CodeDivision Multiple Access (WCDMA) as air interface for the radio-basedcommunication between user equipment (UE), in form of a mobile terminal,and the base station (BS). The air interface in the Open SystemsInterconnection (OSI) model comprises layers 1 and 2 of the mobilecommunications system, establishing a point-to-point link between the UEand a radio access node (RAN).

HSPA is an integral part of WCDMA. Wide-area mobile coverage can beprovided with HSPA. It does not need any additional spectrum orcarriers. Currently, WCDMA can provide simultaneous voice and dataservices to users on the same carrier. This also applies to HSPA whichmeans that spectrum can be used efficiently. Simulations show that in amoderately loaded system, HSPA can largely reduce the time it takes todownload and to upload large files. The primary benefits of HSPA areimproved end-user experience. In practice, this means shorter UL and DLtimes as a result of higher bit-rates and reduced latency compared toearlier releases of WCDMA. HSPA also benefits operators by reducing theproduction cost per bit. More users can be served with higher bit-ratesat lower production costs.

HSPA is the set of technologies defining the migration path of WCDMAoperators worldwide. The two existing features, High Speed DownlinkPacket Access (HSDPA) and High Speed Uplink Packet Access (HSUPA), inthe HSPA family provides the increased performance by using improvedmodulation schemes and by refining the protocols by which handsets andbase stations communicate. These improvements lead to the betterutilization of the existing radio bandwidth provided by UMTS.

High Speed Downlink Packet Access (HSDPA) is the first feature withinHSPA. It is part of the WCDMA Third Generation Partnership Project(3GPP) Release 5 specification. HSDPA provides a new downlink transportchannel that enhances support for high-performance packet dataapplications. It represents the first step in the evolution of WCDMAperformance. HSDPA can deliver an up to 35 fold increase in downlinkdata rates of standard WCDMA networks, enabling users to access theInternet on mobile phones and laptops, at speeds previously associatedwith fixed line DSL.

HSDPA is based on shared channel transmission, which means that somechannel codes and the transmission power in a cell are seen as a commonresource that is dynamically shared between users in the time and codedomains for a more efficient use of available codes and power resourcesin WCDMA. The radio channel conditions experienced by different downlinkcommunication links vary significantly, both in time and betweendifferent positions in the cell. To compensate for rapidly varying radioconditions in the downlink, HSDPA relies on bit-rate adjustment. Thatis, while keeping transmission power constant, it adjusts (by lowering)the data rate by adjusting the modulation.

Along with the HS-DSCH (High Speed Downlink Shared Channel) physicalchannel on which payload data is sent, three new physical channels arealso introduced: HS-SCCH, HS-DPCCH and HS-PDSCH. The High Speed-SharedControl Channel (HS-SCCH) informs the user that data will be sent on theHS-DSCH 2 slots ahead. The Uplink High Speed-Dedicated Physical ControlChannel (HS-DPCCH) carries acknowledgment information and currentchannel quality indicator (CQI) of the user. This value is then used bythe base station to calculate how much data to send to the user deviceson the next transmission. The High Speed-Physical Downlink SharedChannel (HS-PDSCH) is the channel mapped to the above HS-DSCH transportchannel that carries actual user data.

High Speed Uplink Packet Access (HSUPA) is the second feature withinHSPA. It is part of the WCDMA Third Generation Partnership Project(3GPP) Release 6 specification. HSUPA provides a new uplink (UL)transport channel called Enhanced Dedicated CHannel (E-DCH). HSUPAdramatically increases the uplink data traffic rate. It provides apossibility to significantly increase the amount of data uploaded overmobile networks, especially user-generated content. Although a lot of itis downlink oriented, there are still quite a number of applicationsthat will benefit from an improved uplink. These include the sending oflarge e-mail attachments, pictures, video clips, blogs etc. HSUPA isalso known as Enhanced UL. In contrast to HSDPA, the new uplink channelthat is introduced for Enhanced Uplink is not shared between users, butis dedicated to a single user.

FIG. 1 shows a HSUPA network overview. A user terminal 15 communicateswith the core network CN via at least one base station 11. The systemfurther comprises a second base station 10 with a corresponding system.A first radio network controller RNC 12 establishes an E-DCH whichenables uplink data traffic from the user terminal to the base station.The E-DCH carries data for at least one radio network bearer. The term“lu” in FIG. 1 represents the interface between RNC and core network.The term “lub” represents the interface between RNC and the radio basesstation (RBS).

Several new physical channels are added to provide and supporthigh-speed data transmission for the E-DCH. As shown in FIG. 1, two newcode-multiplexed uplink channels are added:

-   -   E-DCH Dedicated Physical Data Channel (E-DPDCH)    -   E-DCH Dedicated Control Channel (E-DPCCH)

E-DPDCH carries the payload data, and the E-DPCCH carries the controlinformation associated to the E-DPDCH. E-DPDCH is used to carry theE-DCH transport channel. There may be zero, one or several E-DPDCH oneach radio link wherein there is at most one E-DPCCH on each radio link.E-DPDCH and E-DPCCH are always transmitted simultaneously. E-DPCCH shallnot be transmitted in a slot unless E-DPDCH is also transmitted in thesame slot.

Similarly, three new channels, see FIG. 1, are added to the downlink forcontrol purposes:

-   -   E-DCH Hybrid Automatic Repeat Request (HARQ) Indicator Channel        (E-HICH) carrying the uplink E-DCH hybrid Acknowledgement (ACK)        and Negative ACK (NACK) indicator.    -   E-DCH Absolute Channel (E-AGCH) carrying absolute grants, which        means that it provides an absolute limitation of the maximum        amount of uplink resources the UE may use.    -   E-DCH Relative Grant Channel (E-RGCH) carrying the uplink E-DCH        relative grants, which means that it controls the resource        limitations by increasing or decreasing the limitations with        respect to the current serving grant.

E-AGCH is only transmitted from the serving cell. E-RGCH and E-HICH aretransmitted from radio links that are part of the serving radio link setand from non-serving radio links.

As shown in FIG. 1 the same E-DCH can be provided both through the firstRNC 12 for the serving cell and through a second RNC (RNC2) 13 for thenon-serving cell. The second RNC 13 serves a separate base station 10with a Node B NB2 and an enhanced UL scheduler (EUL-S2). Except forE-AGCH (which can only be transmitted through the serving cell) all thephysical channels can be transmitted through either of the cells. As analternative one RNC can serve both a serving cell and a non-servingcell. The term “lur” in FIG. 1 represents the interface between thefirst RNC 12 and the second RNC 13. Only one RNC will communicate withthe core network (e.g. the first RNC). The first RNC is in control ofthe connection and handles things like soft handover.

Note that HSUPA channels are added on top of uplink/downlink dedicatedchannels. Each UE 15 therefore additionally carries an uplink anddownlink dedicated physical channel (DPCH), see FIG. 1. In the downlink,a fractional dedicated channel (F-DPCH) can be used alternatively. TheF-DPCH carries control information and is a special case of downlinkDedicated Physical Control Channel (DPCCH). UL might only contain theDPCCH as in FIG. 1. It could also contain a Dedicated Physical DataChannel (DPDCH). The F-DPCH has been introduced in 3GPP release 6 inorder to optimize the downlink codes usage.

The UL scheduling is of central importance for HSUPA. It is provided byan enhanced UL scheduler (EUL-S) located in the Node B, see FIG. 1,close to the air interface. The task of EUL-S is to control the ULresources the UEs 15 in the cell are using. It operates on arequest-grant principle where the UE requests a permission to send dataand the scheduler decides when and how much data an UE is allowed tosend and also how many UEs will be allowed to do so. With the EUL-S ascheme is introduced where the Node B controls the UL transmissions byproviding grants for the UE. The cell appointed as serving cell (serverby Node B NB) is the primary control of the scheduling mechanism bymeans of sending either absolute or relative grants. Thereby the maximumallowed HSUPA transmission is controlled. This effectively limits thetransport block size the UE can select and thus the uplink data trafficrate. It enables the system to admit a larger number of high-data rateusers and rapidly adapts to interference variations—leading to anincrease both in capacity and the likelihood that a user will experiencehigh data rates.

The grants are expressed as power headroom 14, for the E-DPDCH (grant)relative to the DPCCH transmission power (DPCCH (set)), that the UE 15may use for scheduled transmissions. This is illustrated in FIG. 2. Seealso 3GPP 25.214, which for instance describes the relation between theE-DPDCH power and the DPCCH power value. In general, the power headroomdefines the maximum allowed power offset, for instance for E-DPDCH.

Power (watt) is on the Y-axis and time (seconds) on the X-axis, FIG. 2.The DPCCH (set) power varies in dependency on the operation by the UE 15and Node B and follows a SIR target, which will be described in relationto the power control of the DPCCH, DPCCH is power controlled asspecified in the third generation partnership project 3GPP document TS25.214. The E-DPDCH power is converted to a scheduled bit rate by theUE.

As a basic principle of the uplink scheduling mechanism, the UE 15maintains a serving grant which at least represents the maximum E-DPDCHpower offset, the power headroom, which the UE may use in the nexttransmission. This is illustrated in FIG. 3. Power (watt) is on theY-axis and time (seconds) on the X-axis. The line E-DPDCH (used) is thepresent E-DPDCH power offset (read load) used by the channel at acertain time T (seconds). The available uplink power offset determinesthe possible data rate.

The absolute grants (AG₀, AG₁) are used to initialize the schedulingprocess and provide absolute transmit power offset/bit rate (the powerheadroom) for the UE 15. It allows the Node B scheduler to directlyadjust the granted bit rate of UEs under its control. The relativegrants (RG₀) are used for incremental up- or downgrades (by a predefinedstep) from the currently used power headroom (transmit power). Theabsolute grant is carried by the downlink physical channel E-AGCH andthe relative grant is carried by the downlink physical channel E-RGCH.

The power control results in less interference and allows more users onthe same carrier. Power control thus provides more capacity in thenetwork. There is a fast closed loop power control for all the ULsignals to avoid power imbalance between different UE 15 signals and tocombat fast fading. The Node B for instance measures continuously asignal-to-interference ratio (SIR) of the DPCCH transmitted by the UE.SIR relates to the fact that a certain DPCCH power is needed in relationto the interference so that the system is able to decode a data packet.Measurement shall be performed on the DPCCH. SIR is the quotient betweenthe average received modulated carrier power and the average receivedco-channel interference power, e.g. cross-talk from other transmittersthan the useful signal.

This real time SIR measured is compared to a SIR target provided by theRNC 12. The Node B transmits a power control (TPC) command in a downlinkto the UE 15 to increase or decrease the transmit DPCCH power level sothat the real time SIR measured is controlled towards the SIR target.This is for instance described in GB 2336740. The basic step is +/−1dB/slot and eventually 2 dB. With this power control, the signals fromdifferent UEs can be received with the required quality at changingconditions.

All other physical channels are related to the DPCCH by means of theconfigured power offsets. The configuration of the power offset forE-DPDCH depends on the amount of data presently transmitted UL. Ingeneral DPCCH forms the basis for the rapid power control (1500 Hz +/−1dB at each occasion). Dependent on the amount of data transmittedmomentary (for instance in one frame or subframe for E-DPDCH) a poweroffset is decided for instance for the E-DPDCH. This power offset can besignalled via the control signalling to the UE 15 but can also becalculated by the UE from an extrapolation or interpolation from alimited number of reference points.

For E-DPDCH the power relates to the power level of DPCCH by the poweroffset. This power offset varies and is reconfigured continuously by theUE 15 and the RBS simultaneously. The real time value for the E-DPDCHpower is calculated on the basis of the DPCCH power by the power offset.The E-DPDCH power if defined as the DPCCH power+the power offset forE-DPDCH. This power offset depends on the amount of data that should besent in a certain TTI (Transmission Time Interval).

There is a capacity trade-off for the SIR on the DPCCH. Moreover, ifDPCCH is increased the other channels are also increased, e.g. poweroffset on E-DPDCH. If the channel estimation (number of components,relative joint relationship) is optimized it is also possible to performa maximum ratio combining—MRC, which means that the data bits can bedecoded with the lowest possible SIR. The quality of the channelestimate depends on the SIR for the control bits (pilot bits on DPCCH)on which the estimation is based. The consequence is that therequirement on SIR for the data bits can be reduced if SIR for thecontrol bits is increased.

At high power offsets for the other physical UL channels, in this caseE-DPDCH in particular, the drawbacks relating to the increase of SIR forDPCCH is low compared to the benefits relating to improved channelestimation. A reduction of e.g. E-DPDCH power (due to improved_channelestimation) from a high offset creates a relatively large benefit. Ahigh SIR target for DPCCH is beneficial to enable an improved channelestimate (estimated on the DPCCH) which will lower the required SIR forthe E-DPDCH and thus the E-DCH load is reduced.

Raising the SIR target for DPCCH results in an improved channelestimate, but since SIR is the quotient between the channel power andthe average received co-channel interference power, a raised SIRincreases the_DPCCH power.

This result in the problem that at low power for the E-DPDCH thedrawbacks relating to raising the DPCCH (by raising the SIR target forthe DPCCH) can become significant compared to the benefits relating toan improved channel estimation (improved performance for E-DPDCH. Areduction of e.g. E-DPDCH (due to channel estimation) creates arelatively small benefit. The extra load in DPCCH at low power (grants)can not be motivated by the reduced E-DCH load (due to the low poweroffset), since the E-DCH load is anyway rather low.

The relationship between the E-DCH load and the DPCCH load isillustrated in FIG. 4. Line C relates to high E-DCH load (high grant),line A to low E-DCH load (low grant) and B to DPCCH. Load is on theY-axis and SIR on the X-axis. Here it can be seen that in point H, whichrelates to high grant, the extra load in DPCCH (due to higher SIR whichimproves the channel estimate) can be motivated because of the reducedE-DCH load. In point L, which relates to low grant, the extra load inDPDCH can not be motivated by the reduced E-DCH load. The reason is thatthe E-DCH load is anyway rather low.

SUMMARY

The object of the present invention is to solve the above problem by amethod and an enhanced UL telecommunication system for power control anda base station and a user terminal in the system enabling said method.

The problem is solved by means of a method for power control in anenhanced uplink (UL) telecommunication system. The system comprises atleast one first radio network controller (RNC) and at least one firstbase station which enables wireless communication with at least onefirst user terminal. The power for an uplink Dedicated Physical ControlChannel (DPCCH) in a first enhanced UL transport channel (E-DCH) iscontrolled. The control is made by the first base station on the basisof a signal to interference ratio (SIR) target value sent by the firstRNC. Thereby, the SIR real time value for the UL DPCCH is controlledtowards the target value.

The first user terminal and the first base station further calculate apower for at least an Enhanced Dedicated Physical Data Channel (E-DPDCH)in the first E-DCH, which power is defined as the sum of the DPCCH powerand a power offset. The calculation is at least based on a power offsetconfiguration and an absolute grant provided by the first base station,which grant at least set the maximum E-DPDCH power. The first userterminal further transmits the uplink data traffic on the first E-DCHwith the controlled DPCCH power and the calculated E-DPDCH power.

What particularly characterises the method according to the presentinvention is that when the first base station and the first userterminal detects that the E-DPDCH absolute grant is reduced below orincreased above a grant threshold, the base station changes the SIRtarget value. Further, the first base station and the first userterminal compensates the change of the target value by recalculating atleast the E-DPDCH power so that the power reflects both the changedDPCCH power resulting from the changed SIR target value and theimprovement due to optimized channel estimation in case of changed SIRreal time value.

The problem is also solved by means of an enhanced uplink (UL)telecommunication system comprising mechanisms arranged for powercontrol. The system comprises at least one first radio networkcontroller (RNC) and at least one first base station enabling wirelesscommunication with at least one first user terminal. The first basestation (11) comprises a mechanism arranged for controlling the powerfor an uplink Dedicated Physical Control Channel (DPCCH) in a firstenhanced UL transport channel (E-DCH). The control is made on the basisof a signal to interference ratio (SIR) target value sent by the firstRNC (12), so that the SIR real time value for the UL DPCCH is controlledtowards the target value.

A mechanism in the first user terminal and the first base stationmechanism are arranged for calculating a power for at least an EnhancedDedicated Physical Data Channel (E-DPDCH) in the first E-DCH, whichpower is defined as the sum of the DPCCH power and a power offset. Thecalculation is at least based on a power offset configuration and anabsolute grant provided by the first base station, which grant at leastset the maximum E-DPDCH power. The first user terminal mechanism isarranged for transmitting the uplink data traffic on the first E-DCHwith the controlled DPCCH power and the calculated E-DPDCH power.

What particularly characterizes the system of the present invention isthat the first base station mechanism is arranged for changing the SIRtarget value when the first base station and the first user terminaldetects that the E-DPDCH absolute grant is reduced below or increasedabove a certain value. Further, the first base station mechanism and thefirst user terminal mechanism are arranged for compensating the changeof the target value by recalculating at least the E-DPDCH power so thatthe power reflects both the changed DPCCH power, resulting from thechanged SIR target value, and the improvement due to optimized channelestimation in case of changed SIR real time value.

The problem is further solved by means of a base station comprising amechanism arranged for power control in an enhanced uplink (UL)telecommunication system. The system further comprises at least onefirst radio network controller (RNC), the at least one first basestation enabling wireless communication with at least one first userterminal. The first base station (11) mechanism is arranged forcontrolling the power for an uplink Dedicated Physical Control Channel(DPCCH) in a first enhanced UL transport channel (E-DCH). The control ismade on the basis of a signal to interference ratio (SIR) target valuesent by the first RNC (12), so that the SIR real time value for the ULDPCCH is controlled towards the target value. The first base stationmechanism is arranged for calculating a power for at least an EnhancedDedicated Physical Data Channel (E-DPDCH) in the first E-DCH, whichpower is defined as the sum of the DPCCH power and a power offset. Thecalculation is at least based on a power offset configuration and anabsolute grant provided by the first base station, which grant at leastset the maximum E-DPDCH power.

What particularly characterizes the first base station mechanismaccording to the present invention is that it is arranged for changingthe SIR target value when the first base station detects that theE-DPDCH absolute grant is reduced below or increased above a certainvalue. Further, the first base station mechanism is arranged forcompensating the change of the target value by recalculating at leastthe E-DPDCH power so that the power reflects both the changed DPCCHpower, resulting from the changed SIR target value, and the improvementdue to optimized channel estimation in case of changed SIR real timevalue.

The problem is finally solved by means of a user terminal comprising amechanism arranged for power control in an enhanced uplink (UL)telecommunication system. The system further comprises at least onefirst radio network controller (RNC) and at least one first base stationenabling wireless communication with at least one first user terminal(15). The first base station controls the power for an uplink DedicatedPhysical Control

Channel (DPCCH) in a first enhanced UL transport channel (E-DCH) on thebasis of a signal to interference ratio (SIR) target value sent by thefirst RNC (12), so that the SIR real time value for the UL DPCCH iscontrolled towards the target value.

The first user terminal mechanism is arranged for calculating a powerfor at least an Enhanced Dedicated Physical Data Channel (E-DPDCH) inthe first E-DCH, which power is defined as the sum of the DPCCH powerand a power offset. The calculation is at least based on a power offsetconfiguration and an absolute grant provided by the first base station,which grant at least set the maximum E-DPDCH power. The first userterminal (15) mechanism is arranged for transmitting the uplink datatraffic on the first E-DCH with the controlled DPPCH power and thecalculated E-DPDCH power.

What particularly characterizes the first user terminal mechanismaccording to the present invention is that it is further arranged forchanging the SIR target value when the first base station detects thatthe E-DPDCH absolute grant is reduced below or increased above a grantthreshold. The first user terminal mechanism is arranged forcompensating the change of the target value by recalculating at leastthe E-DPDCH power, so that the power reflects both the changed DPCCHpower resulting from the changed SIR target value and the improvementdue to optimized channel estimation in case of changed SIR real timevalue.

The solution provides a possibility to use the trade-off between SIR andthe E-DCH power to improve the UL capacity to some degree. It provides amechanism to determine when it is beneficial to operate at a lower SIRtarget together with a mechanism for configuring this in the UE 15.

Reducing the SIR target by a configured amount when the base stationknows that the UE will only use low power offsets for at least theE-DPDCH, and compensate this in the configuration of the power offsetsfor at least the E-DPDCH will save some of the uplink interferenceheadroom. Moreover, increasing the SIR target and compensating the poweroffset for this when the UE will be able to use high power offsets forthe E-DPDCH, will also optimize the usage of the UL interferenceheadroom.

Moreover, by using a few parameters signalled from the RNC to the UE andthe Node B it is possible to exploit the capacity trade-off for SIRtarget and power offsets for primarily E-DPDCH.

BRIEF DESCRIPTION OF DRAWINGS

In the following text the invention will be described in detail withreference to the attached drawings. These drawings are used forillustration only and do not in any way limit the scope of theinvention:

FIG. 1 shows a HSUPA network overview.

FIG. 2 shows the power headroom related to the DPCCH power via scheduledgrant.

FIG. 3 shows the absolute and relative scheduled grants.

FIG. 4 shows the principles for SIR trade-off in E-DCH power control.

FIG. 5 shows a simplified HSUPA network overview.

FIG. 6 shows the base station and the UE operation.

FIG. 7 shows the RNC 12 signalling of the power offset configuration.

FIG. 8 shows the performance of the first base station

FIG. 9 shows the performance of the first user terminal

DETAILED DESCRIPTION

The invention will now be described in detail with reference toembodiments described in the detailed description and shown in thedrawings.

The embodiments refer to a method and a telecommunication system forpower control, and a base station and a user terminal in the systemenabling said method. The system and the base station in the system areadapted to perform the method steps as described in the method. Itshould be understood by a person skilled in the art that the fact thesystem and in particular the system parts perform a method step meansthat it is adapted to perform said step. This is enabled by introducingnew mechanisms into the system parts, the new mechanisms being arrangedfor performing the method steps described herein.

FIGS. 1 and 5 shows a HSUPA network overview. A user terminal 15communicates with the core network CN via a base station 11. A radionetwork controller RNC 12 establishes an Enhanced Dedicated Channel(E-DCH) which enables uplink data traffic from the user terminal 15 tothe base station, the first E-DCH carrying data for at least one radioaccess bearer (RAB).

The present invention relates to a method for power control in anenhanced uplink (UL) telecommunication system, corresponding to a HSUPAsystem. The HSUPA system comprises at least one first base station 11which enables wireless communication, with a first or more userterminals 15.

A first radio network controller RNC 12 establishes (more than one RNCcan be involved) at least a first enhanced UL transport channel (E-DCH),which enables uplink data traffic with a certain data rate from thefirst user terminal 15 to the first base station 10. The RNC mayestablish E-DCH channels also to other base stations. The E-DCH carriesdata for at least one radio access bearer (RAB). The E-DCH is used fordata and control signalling between the user terminal 15 and the corenetwork CN, when the data transmission starts.

The power for an uplink Dedicated Physical Control Channel—DPCCH in thefirst E-DCH is controlled by the first base station 11 on the basis of asignal to interference ratio (SIR) target value sent by the first RNC(12) so that the SIR real time value for the UL DPCCH is controlledtowards the target value.

The Node B NB in the base station 11 measures continuously the SIR realtime value of the DPCCH transmitted by the first user terminal 15. SIRrelates to the fact that a certain DPCCH power is needed in relation tothe interference so that the system is able to decode a data packet. Itis the quotient between the average received modulated carrier power andthe average received co-channel interference power e.g. cross-talk fromother transmitters than the useful signal. This real time SIR measuredis compared to a SIR target provided by the RNC 12.

The first user terminal 15 and the first base station 11 calculate apower for at least an Enhanced Dedicated Physical Data Channel (E-DPDCH)in the first E-DCH. The power is defined the sum of the DPCCH power anda power offset. The calculation is at least based on a power offsetconfiguration provided by the first RNC 12 and an absolute grantprovided by the base station 11. The grant at least set the maximumE-DPDCH power.

This means that the DPCCH power also regulates the power, e.g. forE-DPDCH, for a certain rate, since this physical channel is dependent onDPCCH by a power offset. This offset is defined in 3GPP standard 25.214.The basis for calculating the power offset is defined in the poweroffset configuration and the E-DPDCH power is calculated as the DPCCHpower+the power offset for E-DPDCH.

As a basic principle of the uplink scheduling mechanism, the first userterminal 15 maintains a serving grant which represents the maximumE-DPDCH power offset, the power headroom, which the first user terminal15 may use in the next transmission, see FIGS. 2-3 and the correspondingparts of the description. The absolute grant is used to set the maximumscheduled grant. The DPCCH power and the power, e.g. for E-DPDCH,corresponds to a scheduled bit rate possibly sent by the first userterminal 15 which means that the grant defines the maximum bit rate UL.

The momentary E-DPDCH power offset (relative to DPCCH) is described by again factor, and depends on the amount of data presently transmitted UL.

The first user terminal (15) transmits the uplink data traffic on thefirst E-DCH with the controlled DPCCH power and the calculated E-DPDCHpower. This means that DPCCH is transmitted with the power set by theinner loop power control (TPC) and the other physical channels, e.g.E-DPDCH, is transmitted with the power calculated on the basis of thepower offset configuration.

There is a capacity trade-off for the SIR on the DPCCH. Moreover, ifDPCCH is increased the other channels are also increased, e.g. powerlevel on E-DPDCH. If the channel estimation (number of components,relative joint relationship) is optimized it is also possible to performa maximum ratio combining (MRC), which means that the data bits can bedecoded with the lowest possible SIR. The quality of the channelestimate depends on the SIR for the control bits (pilot bits on DPCCH)on which the estimation is based. The consequence is that therequirement on SIR for the data bits can be reduced if SIR for thecontrol bits is increased. At high power, the drawbacks relating to theincrease of SIR for DPCCH is low compared to the benefits relating to animproved channel estimation.

However, the problem is that at low power for the E-DPDCH, the drawbacksrelating to raising the DPCCH (by raising the SIR target for the DPCCH)can become significant compared to the benefits relating to an improvedchannel estimation (improved performance for E-DPDCH). The extra load inDPCCH at low E-DPDCH power (grants) can not be motivated by the reducedE-DCH load (due to the low power offset), since the E-DCH load is anywayrather low.

The relationship between the E-DCH load and the DPCCH load isillustrated in FIG. 4. Line C relates to high E-DCH load (high grant),line A to low E-DCH load (low grant) and B to DPCCH. Load is on theY-axis and SIR on the X-axis. Here it can be seen that in point H, whichrelates to high grant, the extra load in DPCCH (due to higher SIR whichimproves the channel estimate) can be motivated because of the reducedE-DCH load. In point L, which relates to low grant, the extra load inDPDCH can not be motivated by the reduced E-DCH load. The reason is thatthe E-DCH load is anyway rather low.

This problem is solved by the following means. When the first basestation 11 and the first user terminal 15 detects that the E-DPDCHabsolute grant is reduced below or increased above a grant threshold,see FIG. 4, the SIR target value is changed by the base station 11.Moreover, to benefit from the optimized channel estimation, the firstbase station 11 and the first user terminal 15 compensates the change ofthe target value. This is done by recalculating at least the E-DPDCHpower so that the power reflects both the changed DPCCH power resultingfrom the changed SIR target value and the improvement due to optimizedchannel estimation in case of changed SIR real time value.

The power offset configuration provided by the RNC comprises informationabout the at least one grant threshold for the E-DPDCH absolute grantand reconfiguration information for each threshold on which basis theSIR target value is changed and at least the E-DPDCH power isrecalculated. The E-DPDCH power is recalculated by recalculating thepower offset on the basis of the reconfiguration information.

The RNC via the power offset configuration informs both the first userterminal 15 and the first radio base station about the grant thresholdvalues for the E-DPDCH absolute grant/-s, at which the SIR target andthe E-DPDCH should be changed/recalculated. The recalculation isperformed by changing the power offset. It will be described later howthe SIR target is changed and the power offset is recalculated.

FIG. 7 shows the RNC 12 signalling of the power offset configuration tosupport configuration and reconfiguration of grant threshold in firstuser terminal 15 and the first base station BS 11. Reference 1 and 2represents the setup request for the configuration and 3,4 thereconfiguration of the power offset configuration. The setup orreconfiguration may both be used to define the triggering threshold andthe changes to apply in SIR target and power offsets, the actual use ofthe changes to apply to SIR target and power offsets is not triggered byany RNC signal.

The first base station performs at least a first downlink transmissionincluding a first power control command to the first user terminal 15 tocontrol the DPCCH power The DPCCH power is controlled by increasing ordecreasing the transmit DPCCH power so that the real time SIR measuredis controlled towards the SIR target. The basic control step is +/−1dB/slot and eventually 2 dB.

The first user terminal 15 and the first base station 11 recalculates apower for at least the High Speed Dedicated Physical Data Channel(HS-DPDCH), the Enhanced Dedicated Physical Data Channel (E-DPDCH) andthe Enhanced Dedicated Physical Control Channel (E-DPCCH) on the basisof the power for the DPCCH. The calculation is based on the power offsetconfiguration provided by the RNC (12).

The particular control performed when the first base station 11 and thefirst user terminal 15 detects that the E-DPDCH absolute grant isreduced below or increased above a grant threshold will now bedescribed. This is illustrated in FIG. 6. The basic idea in the presentinvention are two steps:

-   -   1. The SIR target value is changed by the base station 11.    -   2. To benefit from the optimized channel estimation, the first        base station and the first user terminal 15 compensates the        change of the target value. This is done by recalculating at        least the E-DPDCH power so that the power reflects both the        changed DPCCH power and the improvement due to optimized channel        estimation.

The change of the SIR real time value and the recalculating of at leastthe E-DPDCH power are performed when detecting that the E-DPDCH absolutegrant is reduced below or increased above the grant threshold. Theexecution of the power offset recalculation is executed by the firstuser terminal 15 and the base station 11 on the basis of the poweroffset configuration.

The performance by the first base station 11 is shown in FIG. 8.“Maximum serving grant” is the maximum E-DPDCH power (headroom) allowedby the base station (which provides the absolute grants). The E-DPDCHabsolute grant is provided by the first base station 11 serving theserving cell. The calculation of the E-DPDCH power consequently has toconsider the E-DPDCH absolute grant together with calculating based onthe power offset configuration. The 3GPP standard 25.321 defines themaximum serving grant.

Grant threshold 1, see FIG. 8, is a certain grant threshold for theE-DPDCH absolute grant. When the first base station 11 detects that atleast the E-DPDCH absolute grant is reduced below or increased above thethreshold the steps of changing SIR and recalculating at least theE-DPDCH power is performed. The power offset configuration provided bythe RNC preferably comprises more than one grant threshold. This meansthat at certain E-DPDCH absolute grants values these steps areperformed. Moreover, it should also be understood by the skilled personthat also when maximum serving grant is larger than a grant threshold(for instance grant threshold 1) these steps are performed.

In practise this means that when the absolute grant and consequently theE-DPDCH power increases, the SIR target is increased by the first basestation 11 and at least the E-DPDCH real time power is decreased. Andwhen the E-DPDCH is decreased the SIR target is decreased and at leastthe E-DPDCH real time power is increased.

Reference power offset k, see FIG. 8, is used to calculate the E-DPDCHpower for a certain rate. What happens is that when the first userterminal 15 and the first base station 11 detects that the absolutegrant for the E-DPDCH is increased above or decreased below a grantthreshold, they perform a recalculation of the reference power offset onthe basis of the reconfiguration information in the power offsetconfiguration. Correspondingly, a recalculation of the power offset forthe physical channel HS-DPCCH and E-DPCCH is performed on the basis ofthe reconfiguration information in the power offset configuration.Letter “k” only a variable.

The performance by the first user terminal 15 is illustrated in FIG. 9.This means that the first user terminal 15 and the first base station 11synchronized recalculates the reference power offset, the HS-DPCCH poweroffset and the E-DPCCH power offset. Both have been informed by the RNCthe recalculation policy for the offsets when receiving the power offsetconfiguration. Consequently, they both know the delta power offset thatshould be used when detecting that the E-DPDCH absolute grant is reducedbelow or increased above the grant threshold. The delta power offset isconfigured by the RNC which know how to compensate a changed SIR target.The delta power offset can be either positive (when SIR target isdecreased) or negative (when SIR target is increased). They arepreferably individual for the respective physical channel and thereforenamed 1, 2 and 3.

The first base station 11 changes the SIR target value and the basestation synchronously with the first user terminal 15 (see FIGS. 8 and9) compensates the change of the target value if the maximum servinggrant is lower than at least one threshold value. This is illustrated inFIG. 6. If maximum serving grant is lower than a grant threshold 1, seebox “If maximum serving grant<grant threshold 1”, the change of the SIRtarget value and the reconfiguration is performed, see box RECONFIG, bythe first base station 11. This means that the first base station 11detects that the absolute grant is reduced below the grant threshold acertain value and reduces the signal interference value by configuredamount.

As an alternative if the maximum serving grant is higher than the grantthreshold 1 a change of the SIR target value and the reconfiguration isperformed. This means that the first base station 11 detects that theabsolute grant is increased above a certain value and increases the SIRtarget value by a configured amount. Increasing SIR target andcompensating the power offsets for this when the first user terminalwill be able to use high power offsets for the E-DPDCH will optimize theusage of the UL interference headroom as well.

The SIR target value is changed by the first base station (11) by addinga delta SIR real time value to the present SIR target value (set by theRNC 12).

This can be expressed as (see FIG. 8):

SIR target=(SIR target as controlled by the RNC)+(delta SIR 1)

The E-DPDCH power is recalculated by the first base station 11 and thefirst user terminal 15 by adding a delta power offset value to thepresent power offset for each reference point.

This can be expressed as (see FIGS. 8 and 9):

Reference power offset k=(reference power offset k as controlled by theRNC)+delta power offset 1 (for all k)

Moreover for HS-DPCCH it can be expressed as (FIGS. 8 and 9):

HS-DPCCH power offset=(hs-dpcch power offset as controlled by theRNC)+delta power offset 2

Finally for E-DPCCH it can be expressed as (FIGS. 8 and 9):

E-DPCCH power offset=(e-dpcch power offset as controlled by theRNC)+delta power offset 3

As shown the first base station (11) and the first user terminal 15recalculates the power for at least the High Speed Dedicated PhysicalData Channel (HS-DPDCH), the Enhanced Dedicated Physical Data Channel(E-DPDCH) and/or the Enhanced Dedicated Physical Control Channel(E-DPCCH) by adding a delta power offset value to the power offset.

It will be appreciated by the person skilled in the art that variousmodifications may be made to the above-described embodiments withoutdeparting from the scope of the present invention. For instance, theconcept is not limited to a single grant threshold. Moreover, the deltapower offsets may be the instead of different thresholds. Finally, botha reduction and an increase of the SIR target by a configured amount arepossible in order to optimize the usage of the UL interference headroom.

1. A method for power control in an enhanced uplink (UL)telecommunication system comprising at least one first radio networkcontroller (RNC) and at least one first base station enabling wirelesscommunication with at least one first user terminal, the power for anuplink Dedicated Physical Control Channel (DPCCH) in a first enhanced ULtransport channel (E-DCH) being controlled by the first base station onthe basis of a signal to interference ratio (SIR) target value sent bythe first RNC so that the SIR real time value for the UL DPCCH iscontrolled towards the target value, the first user terminal and thefirst base station calculating a power for at least an EnhancedDedicated Physical Data Channel (E-DPDCH) in the first E-DCH, the powerbeing defined as the sum of the DPCCH power and a power offset, thecalculation at least being based on a power offset configuration and anabsolute grant provided by the first base station, which grant at leastset the maximum E-DPDCH power, the first user terminal transmitting theuplink data traffic on the first E-DCH with the controlled DPCCH powerand the calculated E-DPDCH power, wherein when the first base stationand the first user terminal detects that the E-DPDCH absolute grant isreduced below or increased above a grant threshold the base stationchanges the SIR target value, the first base station and the first userterminal compensating the change of the target value by recalculating atleast the E-DPDCH power so that the power reflects both the changedDPCCH power resulting from the changed SIR target value and theimprovement due to optimized channel estimation in case of changed SIRreal time value.
 2. The method according to claim 1 wherein the poweroffset configuration provided by the RNC comprises information about atleast one grant threshold for the E-DPDCH absolute grant andreconfiguration information for each threshold on which basis the SIRtarget value is changed and at least the E-DPDCH power is recalculated.3. The method according to claim 2 wherein the E-DPDCH power isrecalculated by recalculating the power offset on the basis of thereconfiguration information.
 4. The method according to claim 1 whereinthe first base station performs at least a first downlink transmissionincluding a first power control command to the first user terminal tocontrol the DPCCH power.
 5. The method according to claim 1 wherein thefirst user terminal and the first base station further recalculates apower offset for at least the High Speed Dedicated Physical Data Channel(HS-DPDCH), the Enhanced Dedicated Physical Data Channel (E-DPDCH) andthe Enhanced Dedicated Physical Control Channel (E-DPCCH) on the basisof the DPCCH power, the calculation being based on the power offsetconfiguration provided by the RNC.
 6. The method according to claim 1wherein the first base station when detecting that the E-DPDCH absolutegrant is reduced below a certain value reduces the SIR target value by aconfigured amount.
 7. The method according to claim 1 wherein the firstbase station when detecting that the E-DPDCH absolute grant is increasedabove a certain value increases the SIR target value by a configuredamount.
 8. The method according to claim 6 wherein the SIR target valueis changed by the first base station by adding a delta SIR real timevalue to the present SIR target value.
 9. The method according to claim1 wherein the E-DPDCH power is recalculated by the first base stationand the first user terminal by adding a delta power offset value to thepower offset for each reference point.
 10. The method according to claim9 wherein the first base station and the first user terminalrecalculates the power for at least the High Speed Dedicated PhysicalData Channel (HS-DPDCH), the Enhanced Dedicated Physical Data Channel(E-DPDCH) and the Enhanced Dedicated Physical Control Channel (E-DPCCH)by adding a delta power offset value to the power offset.
 11. Anenhanced uplink (UL) telecommunication system comprising mechanismsarranged for power control, the system comprising at least one firstradio network controller (RNC) and at least one first base stationenabling wireless communication with at least one first user terminal,the first base station comprising a mechanism arranged for controllingthe power for an uplink Dedicated Physical Control Channel (DPCCH) in afirst enhanced UL transport channel (E-DCH) on the basis of a signal tointerference ratio (SIR) target value sent by the first RNC so that theSIR real time value for the UL DPCCH is controlled towards the targetvalue, a mechanism in the first user terminal and the first base stationmechanism are arranged for calculating a power for at least an EnhancedDedicated Physical Data Channel (E-DPDCH) in the first E-DCH, the powerbeing defined as the sum of the DPCCH power and a power offset, thecalculation at least being based on a power offset configuration and anabsolute grant provided by the first base station, which grant at leastset the maximum E-DPDCH power, the first user terminal mechanism isarranged for transmitting the uplink data traffic on the first E-DCHwith the controlled DPCCH power and the calculated E-DPDCH power,wherein the first base station mechanism is arranged for changing theSIR target value when the first base station and the first user terminaldetects that the E-DPDCH absolute grant is reduced below or increasedabove a certain value, the first base station mechanism and the firstuser terminal mechanism are arranged for compensating the change of thetarget value by recalculating at least the E-DPDCH power so that thepower reflects both the changed DPCCH power resulting from the changedSIR target value and the improvement due to optimized channel estimationin case of changed SIR real time value.
 12. The enhanced ULtelecommunication system according to claim 11 wherein the first basestation mechanism is arranged for performing at least a first downlinktransmission including a first power control command to the first userterminal to control the DPCCH power.
 13. The enhanced ULtelecommunication system according to claim 11 wherein the first userterminal mechanism and the first base station mechanism are arranged forrecalculating a power offset for at least the High Speed DedicatedPhysical Data Channel (HS-DPDCH), the Enhanced Dedicated Physical DataChannel (E-DPDCH) and the Enhanced Dedicated Physical Control Channel(E-DPCCH) on the basis of the DPCCH power, the calculation being basedon the power offset configuration provided by the RNC.
 14. The enhancedUL telecommunication system according to claim 11 wherein the first basestation mechanism is arranged for reducing the SIR target value by aconfigured amount when detecting that the E-DPDCH absolute grant isreduced below a certain value
 15. The enhanced UL telecommunicationsystem according to claim 11 wherein the first base station mechanism isarranged for increasing the SIR target value by a configured amount whendetecting that the E-DPDCH absolute grant is increased above a certainvalue.
 16. The enhanced UL telecommunication system according to claim15 wherein the first base station mechanism is arranged for changing theSIR target value by adding a delta SIR real time value to the presentSIR target value.
 17. The enhanced UL telecommunication system accordingto claim 13 wherein the first base station mechanism and the first userterminal mechanism are arranged for recalculating the E-DPDCH power byadding a delta power offset to the present offset for each referencepoint.
 18. The enhanced UL telecommunication system according to claim17 wherein the first base station mechanism and the first user terminalmechanism are arranged for recalculating the power for at least the HighSpeed Dedicated Physical Data Channel (HS-DPDCH), the Enhanced DedicatedPhysical Data Channel (E-DPDCH) and/or the Enhanced Dedicated PhysicalControl Channel (E-DPCCH) by adding a delta power offset value to thepower offset.
 19. A base station comprising a mechanism arranged forpower control in an enhanced uplink (UL) telecommunication systemfurther comprising at least one first radio network controller (RNC),the at least one first base station enabling wireless communication withat least one first user terminal, the first base station mechanism isarranged for controlling the power for an uplink Dedicated PhysicalControl Channel (DPCCH) in a first enhanced UL transport channel (E-DCH)on the basis of a signal to interference ratio (SIR) target value sentby the first RNC, so that the SIR real time value for the UL DPCCH iscontrolled towards the target value, the first base station mechanism isarranged for calculating a power for at least an Enhanced DedicatedPhysical Data Channel (E-DPDCH), the power being defined as the sum ofthe DPCCH power and a power offset, the calculation at least being basedon a power offset configuration and an absolute grant provided by thefirst base station, which grant at least set the maximum E-DPDCH power,wherein the first base station mechanism is arranged for changing theSIR target value when the first base station and the first user terminaldetects that the E-DPDCH absolute grant is reduced below or increasedabove a grant threshold, the first base station mechanism is arrangedfor compensating the change of the target value by recalculating atleast the E-DPDCH power so that the power reflects both the changedDPCCH power resulting from the changed SIR target value and theimprovement due to optimized channel estimation in case of changed SIRreal time value.
 20. The base station according to claim 19 wherein thefirst base station mechanism is arranged for performing at least a firstdownlink transmission including a first power control command to thefirst user terminal to control the DPCCH power.
 21. The base stationaccording to claim 19 wherein the first base station mechanism isarranged for recalculating a power offset for at least the High SpeedDedicated Physical Data Channel (HS-DPDCH), the Enhanced DedicatedPhysical Data Channel (E-DPDCH) and the Enhanced Dedicated PhysicalControl Channel (E-DPCCH) on the basis of the DPCCH power, thecalculation being based on the power offset configuration provided bythe RNC.
 22. The base station according to claim 19 wherein the firstbase station mechanism is arranged for reducing the SIR target value bya configured amount when detecting that the E-DPDCH absolute grant isreduced below a certain value
 23. The base station according to claim 19wherein the first base station mechanism is arranged for increasing theSIR target value by a configured amount when detecting that the E-DPDCHabsolute grant is increased above a certain value.
 24. The base stationaccording to claim 22 wherein the first base station mechanism isarranged for changing the SIR target value by adding a delta SIR realtime value to the present SIR target value.
 25. The base stationaccording to claim 19 wherein the first base station mechanism isarranged for recalculating the E-DPDCH power by adding a delta poweroffset value to the present offset for each reference point.
 26. Theenhanced UL telecommunication system according to claim 25 wherein thefirst base station mechanism is arranged for recalculating the power forat least the High Speed Dedicated Physical Data Channel (HS-DPDCH), theEnhanced Dedicated Physical Data Channel (E-DPDCH) and/or the EnhancedDedicated Physical Control Channel (E-DPCCH) by adding a delta poweroffset value to the power offset.
 27. A user terminal comprising amechanism arranged for power control in an enhanced uplink (UL)telecommunication system further comprising at least one first radionetwork controller (RNC) and at least one first base station enablingwireless communication with at least one first user terminal, the firstbase station controlling the power for an uplink Dedicated PhysicalControl Channel (DPCCH) in a first enhanced UL transport channel (E-DCH)on the basis of a signal to interference ratio (SIR) target value sentby the first RNC, so that the SIR real time value for the UL DPCCH iscontrolled towards the target value, the first user terminal mechanismis arranged for calculating a power for at least an Enhanced DedicatedPhysical Data Channel (E-DPDCH), the power being defined as the sum ofthe DPCCH power and a power offset, the calculation at least being basedon a power offset configuration and an absolute grant provided by thefirst base station, which grant at least set the maximum E-DPDCH power,the first user terminal mechanism is arranged for transmitting theuplink data traffic on the first E-DCH with the controlled DPPCH powerand the calculated E-DPDCH power, wherein the first user terminalmechanism is arranged for changing the SIR target value when the firstbase station detects that the E-DPDCH absolute grant is reduced below orincreased above a grant threshold, the first user terminal mechanism isarranged for compensating the change of the target value byrecalculating at least the E-DPDCH power so that the power reflects boththe changed DPCCH power resulting from the changed SIR target value andthe improvement due to optimized channel estimation in case of changedSIR real time value.
 28. The user terminal according to claim 27 whereinthe user terminal mechanism is arranged for recalculating a power offsetfor at least the High Speed Dedicated Physical Data Channel (HS-DPDCH),the Enhanced Dedicated Physical Data Channel (E-DPDCH) and the EnhancedDedicated Physical Control Channel (E-DPCCH) on the basis of the DPCCHpower, the calculation being based on the power offset configurationprovided by the RNC.
 29. The user terminal according to claim 27 whereinthe A user terminal mechanism is arranged for recalculating the E-DPDCHpower by adding a delta power offset value to the present offset foreach reference point.
 30. The user terminal according to claim 29wherein the A user terminal mechanism is arranged for recalculating thepower for at least the High Speed Dedicated Physical Data Channel(HS-DPDCH), the Enhanced Dedicated Physical Data Channel (E-DPDCH)and/or the Enhanced Dedicated Physical Control Channel (E-DPCCH) byadding a delta power offset value to the power offset.